1. Field of the Invention
The present invention relates to a polishing pad for use in chemical mechanical polishing, use thereof and method for making the same.
2. Description of the Related Art
Chemical mechanical polishing (CMP) is a procedure for planarizing the surface of a substrate with a polishing pad. CMP is generally applied in polishing lenses, mirrors, substrates of liquid crystal displays, silicon wafers, and oxidation and/or metal layers on silicon wafers.
Taking silicon wafers as an example, ingots of monocrystalline silicon are sliced first. The wafers are usually lapped to make them flat for subsequently chemical etching. A polishing process is required after the etching process. During the polishing process, a polishing pad together with slurry reacts chemically with the silicon atoms on the surface of the wafer to make the reacted surface softer than the underlying silicon. Furthermore, the reacted surface is continually wiped away, causing fresh silicon to be exposed to the slurry and the polishing pad.
U.S. Pat. No. 6,358,130 discloses a conventional polishing pad for use with slurry. The conventional polishing pad has a polishing layer and a window in an opening through the polishing layer. The undersurfaces of the polishing layer and window are covered by an underlying fluid-impermeable layer. The conventional polishing pad further comprises adhesive on the fluid-impermeable layer forming respective bond seals between the polishing layer and the window and a lower backing layer. The adhesive and the fluid impermeable layer resist wetting of an interface between the adhesive and each of the polishing layer, the window and the fluid-impermeable layer in the conventional polishing pad. An advantage is that the fluid-impermeable layer, being uninterrupted, avoids a tendency to produce leakage paths due to bending during routine handling, or due to exertion of polishing pressure during use of the polishing pad, or due to small voids or gaps in the adhesive. A further advantage is that the bond seals minimize wetting by the slurry of the interface between the adhesive and each of the polishing layer, the window and the fluid-impermeable layer.
Because the lower backing layer of the conventional polishing pad usually comprises fibers, the contents of the lower backing layer are not distributed evenly. Also, because the polishing layer of the conventional polishing pad usually comprises elastomers, the contents of the polishing layer are not distributed evenly either. The variations of the thickness of the lower backing layer and polishing pad are easily observed. Besides, the surfaces of the lower backing layer and the polishing pad are not flat and usually rough and undulating. Such features make it difficult for the lower backing layer or polishing pad to attach tightly and completely to the fluid-impermeable layer. Bubbles and vacant space are easily observed in the interface between the lower backing layer and the polishing layer and the fluid-impermeable layer (as shown in FIG. 1). As a result, the slurry easily permeates into the interface between the lower backing layer and the polishing layer and the fluid-impermeable layer via the bubbles and vacant space. Therefore, the lifespan of the conventional polishing pad is shortened. The effect and efficiency of chemical mechanical polishing are both reduced thereby.